[newbie] read an acpi value

[remi.vallez at gmail.com (Rémi Vallez)]

I am working on the subject "wifi and power management on laptops" and
i try to get the battery present rate and battery present voltage.
i know this 2 values are present in the ACPI  (in the table _BST)  but
they are not retrieve by sysctl.

Can you tell me a way to retrieve this values